dBpowerAMP Music Converter R11
dBpowerAMP Music Converter is exactly that.
It embeds into your right-click menu, and you can access the convert command by right-clicking on an MP3 or WAV file.
It has three encoders to choose from: two MP3 encoders and one WAV encoder.
This convertor works with WAV and MP3 files. According to the description we received, it also supports OGG and WMA; unfortunately, neither worked in the stress tests.